Current-regulating apparatus



1,628,678 y 1927' M. MORRISON CURRENT REGULATING APPARATUS Filed Jan. 2. 1922 INVENTOR MONTFORD MORR\SON A TORNEY Patented May 17, 1927.

UNITED STATES.

MONTFORD MORRISON, OF NEW YORK, N. Y.

CURRENT-REGULA'IING APPARATUS.

Application filed January 2, 1922. Serial No. 526,453.

This invention relates to electrical control apparatus and more particularly to means and methods for automatically maintaining an electrical current constant.

The necessity of maintaining an electrical current constant in order to secure the most efficient operation of many types of electrical apparatus is well known. An X-ray tube is an example of an electrical device which should be operated with a steady current on account of the desirability of maintaining constant a desired volume of X-ra s.

To attain stability in electron-disc arge devices, it has long been the practice to utilize variations in the discharge current of the tube to actuate means for keeping constant the supply of electrons at the cathode and thus stabilize the discharge current. Devices employing this principle have been 20 used for many years, especially in Germany,

for maintaining the discharge current constant in X-ray tubes.

An object of this invention is the provision of means for automatically limiting the current in an electrical circuit.

A special object of the invention is the provision of means for maintaining the dis charge current in a hot-cathode X-ray device constant, independent of the specific 30 emissivity of the cathode and of the linevoltage variation.

Other objects will be appreciated upon reading the following specification.

Constant-current regulators of the prior art have consisted, for the most part, of moving elements, which are admitted to be objectionable. The present invention providcs a constant-current regulator or stabilizer which has no moving members and which operates by purely electrical phenomena.

According to'my invention, the current in an electrical circuit is controlled by regulating the-magnitude of an electron stream which exerts an influence on the current to be controlled. The electron stream may be partially or wholly cut out by repulsion or deflection of the electrons due to anelectrostatic field. The repressive or repellant force beingmade a function of the current to be controlled, the magnitude of the electron stream varies with the latter current, i but in an opposite sense, and, since it exerts a control over thesame, the latter will be automatically stabilized. More particularly,

one method of stabilizing an electric current, according to my invention, consists in connecting a three-electrode vacuum electron tube in such manner that the magnitude of the current through the tube determines the current in the main circuit and varies in an inverse ratio with the latter. This inverse relationship is effected by so connecting the tube to auxiliary apparatus that the potential on a third electrode varies with the current in the main circuit, and, by reason of its potential, controls the magnitude of the electron stream.

My invention will be more clearly understood by reference to the following descrip tion taken in connection with the accompanying drawing which is a diagrammatic representation of an embodiment of my new stabilizer, showing its application to a power load, such as an X-ray tube, for the purpose of maintaining the current constant.

Referring to the drawing, a high-tension secondary coil 3 of a transformer 4:, of which a coil 5 is the primary, has one of its terminals connected, by means of a conductor 6, to a primary coil 7 of a transformer 8, another terminal of coil 7 being connected, by means of conductor 9, to a terminal 10 of a mechanical rectifier 11 which is preferably of the sphere and toroid type described and claimed in my copending application Serial No. 460,835, filed April 12, 1921, now Patent No. 1,466,541, August 28, 1923. Another terminal of the secondary coil 3 is connected directly to a terminal 12 of the rectifier 11 by means of a conductor 13. A terminal 14 of the rectifier ll is connectei'l, by means of conductor 15, to a terminal .16 of an X-ray tube 17 which comprises an evacuated envelope 18, preferably consisting of glass. having oppositely extending arms 19 and 20 into which are sealed, respectively, an anode 21 and a cathode 22 which latter is a helical filament of tungsten or other suitable refractory material, connected to leading-in con ductors 23 and 24 so that it may be heated to an. electron-emitting temperature.

The cathode 22 is electrically associated with the rectifier 11 by having the leading in conductor 24 connected, by means of conductor 25, to a terminal 26 of the rectifier, and is adapted to be electrically heated from a transformer 2? by having its leading in conductor 23 connected, by means of conductor 28, to a terminal of the secondary coil '29, and its leading-in conductor 24% connected to the transformer secondary 29 by means of conductor 30 and a three-electrode vacuum electron tube 31. The three-electrode tube 31 comprises an envelope 32 enclosing a plate electrode 33, a grid electrode 34: and a filament 35 which is adapted to be variably heated through conductors 36 and 37 from the transformer secondary 29. The

plate 33 is electrically connected by means i of conductor 38 to the conductor 30 and, by

the same conductor, is connected to the grid 34 through a secondary coil 39 of transformer 8 and a high-resistance element 40.

In the normal operation of the circuit,

a constant voltage unvarying in amplitude is generated in the transformer secondaries 3 and 29, energy from the latter serving to heat the filament ot the three-electrode vacuum tube 31 to an electron-emitting tem perature and to impress a potential on the plate 33 o f the tube 31 by which electrons are caused to fiow from the filament to ondary coil 39, through which the electrons might reach the filament 22 without passing to the plate 33 were not the high resistance 40 placed in series with the grid 34 to prevent the leakage of the electrons through the by-path.

Vhile the normal discharge current is passing through the X-ray tube the electrical constants of the transformer 8 are such that the difference in potential between the plate 33 and the grid 34 allows the full stream of electrons emanating from the fila ment 35 to reach the plate 33 and to pass onto the filament 22 and heat the same by means of rectified or pulsating current. lVhen, however, the line voltage of the transformer & rises above its normal value, as frequently happens in commercial circuits, the electrical connections of the transformer 8 are such that the potential of the grid 34; becomes sufiiciently difli'erent from that of the plate33 or, in other words, more negative than the filament 35, to repel the electrons emanating from the latter. It is obvious thatthe effect of this repulsion'is to reduce the magnitude of the electronic stream and, therefore, to reduce the heating current of the filament 22. Since the discharge current of the Xray tube depends on the temperature of the filament 22, a

" reduction in the temperature of the latter will'deerease the discharge current in the X-ray tube, thus offsetting the tendency oi the abnormal line voltage to send an undesired increase of discharge current through tube.

The filament 22 is supplied with rectified current from a single three-electrode vacuum tube, as shown, but with two such tubes the current to the filament may be alternaling. As to whether the filament is supplied with alternating or pulsating rectified current is not material to the invention, but the use of pulsating current is shown. as the diagram for such an arrangement is simpler. The voltage of 39 tends: to arrest the flow of the filament current and will govern the fiow thereof during the time that the. tube 32 is rectifying. Of course, when there is no current flowing through said tube, there will be no governing action with respect thereto.

In case the line voltage of the transformer lfalls below the normal value, the electrical conditions of the circuit are automatically readjusted in a similar manner, but in an opposite sense, to that described for an increase in line voltage, so that the normal discharge current is restored to the tube.

The stabilizing action described is ell'cetive not only against fluctuations oil? line voltage but against a possible change in the specific emissivity oi the cathode. For example, when the electron emissivity is diminished, which may happen when a slight amount of impurities attack the cathode, the discharge current will fall otll', since the latter is afunction of the specific emissivity oi the cathode. The discharge current through the tube having been decreased, the resultant electrical reiuljustmcnts are the same as those which are b rought about by a decrease in discharge current following a falling oil in line VOlttlgO.

The current control described is especially valuable in X-ray tubes used for therapeutic purposes, inasmuch as the dosage of X-rays applied must b a coniuant quantity in order to avoid possible injury to a patient.

Vhile I have described, in tleuiil. one Form of stabilizer embodying m'y invention and circuit arrangement therefor, minor modifications may easily be made in the same which, however, employ the same underlying principle, and it is desired that it be understood that such modifications come within the scope of this invention as embraced in the appended claims.

\Vhat is claimed is:

1. In combination with an X-ray tube having a hot cathode and an anode across which a high potential is impressed subject to variations in voltage which causes erratic current flow, means for increasing or decreasing the current flow in said tube comprising a three-electrode vacuum elee-.

tron tube, means whereby the grid oi. which Ell] lllll lllii lio is caused to fluctuate in potential corresponding to the changes in potential impressed on said tube circuit.

2. In an electrical circuit the combination of an X-ray device, means for passing a current through said device, a three-electrode vacuum electron tube, and means by which said vacuum tube is governed by the current through the X-ray device for controlling the operation thereof by means of an electrostatic field therein.

3. In an electrical circuit the combination of a hotcath0de vacuum device subject to variations in the quantity of electron discharge therein, a three-electrode vacuum tube, means for establishing an electrostatic field therein responsive to said variations, and connections whereby the temperature of the hot cathode is controlled so that the electron discharge through the vacuum device is maintained substantially constant.

4. An X-ray apparatus comprisin ahotcathode X-ray tube, means for heating the cathode of said tube and means connected to said first mentioned means for controlling the volume of X-rays generated in said tube, the second-mentioned means having an electron stream in circuit and an electrostatic field associated with said first mentioned means which operate to control. the temperature of the cathode of said tube by the action of the electron stream made variable by the action of the electrostatic field.

5. An electric discharge system comprising a hot-cathode tube, a power supply circuit therefor subject to variations, a heating circuit for the cathode of said tube, a threeelectrode vacuum tube in said heating circuit and means automatically responsive to variations in said supply circuit for controlling the discharge current through said vacuum tube.

6. An electric discharge system comprising a hot-cathode tube, a power supply circuit therefor subject to variations, a transformer having its primary coil in said supply circuit, a heating circuit for the cathode of said tube and a three-electrode vacuum tube controlling the current in said heating circuit and electrically connected with the secondary coil of said transformer.

7. An electric discharge system comprising a hot-cathode tube having a power sup ply circuit subject to variations, a trans-- former having its primary coil in said sup-- ply circuit, a heating circuit for the cathode of said tube, a three-electrode vacuum tube in said heating circuit, said vacuum tube comprising an incandescent filament, a grid and a plate enclosed in an evacuated envelope, said grid and said plate being connected to the secondary of said transformer.

8. An electric discharge system comprising a hot-cathode tube having a power supply circuit subject to variations, a transformer having its primary coil in said supply circuit, a heating circuit'tor the cathode of said tube. a three-electrode vacuum tube in said heating circuit, said vacuum tube comprising an incandescent filament, a grid and a plate enclosed in an evacuated envelope, said grid and said plate being connected to the secondary coil of said transformer and high resistance intervening between said secondary coil and said grid.

9. The method of controlling the current from a. hot cathode in an electrical circuit comprising governing the magnitude of an electron stream as part of the circuit serving to heat the cathode by means of an electrostatic field, the intensity of which depends on the current from the hot cathode and tends to reduce that current.

'10. The method of stabilizing the volume of X-rays generated in a hot-cathode X-ra tube comprising controlling the electronemissivity ot the hot cathode of said tube, by automatically varying the magnitude of an electron stream as part of the circuit serving to heat said cathode by means of an electrostatic field dependent upon the electron-emissivity of said hot cathode.

11. The method of regulating the space or electron current in a vacuum tube having an incandescent cathode supplied with current of variable potential, which consists in adjusting the teu'iperature oi. the cathode of said tube with respect to the applied voltage to produce saturation current, producing a second electron discharge, varying the second discliarge in response to the variations of: space current of the first discharge, and controlling the teuijiieral ure of the oath ode. in the tube being regulated, inversely as a function of current variations of the second discharge.

In testimony whereof, I have hereunto subscribed my name this thirtieth day of December, 1921.

MONTITFORU lllORRlSON. 

